1. Field of the Invention
The present invention relates to a light emitting diode and more particularly to a chip type light emitting diode surface-mounted on a printed circuit board and the like.
2. Description of the Prior Art
A chip type light emitting diode has a generally known construction such as shown in FIG. 1. This light emitting diode 1 comprises a base substrate 2 made from a rectangular glass epoxy plate, a first electrode 3 and a second electrode 4 separated from each other and provided at left and right sides of the base substrate 2 as by etching, a light emitting element 5 mounted on an upper surface of the first electrode 3, a bonding wire 6 connecting the light emitting element 5 and the second electrode 4, and a transparent resin sealing member 7 covering the bonding wire 6 and the light emitting element 5 from above.
The light emitting diode 1 of the above construction has found a wide range of applications in recent years, for example, as a backlight source in a liquid crystal display of cellular phones and small electronic devices. In this application an example use of the light emitting diode has a configuration that, as shown in FIG. 2, a mother board 8 for mounting the light emitting diode 1 is formed with an opening 9, and that a pair of left and right electrodes 3, 4 of the light emitting diode 1 are secured by solder 10 to peripheral portions on the back surface of the opening 9 so that light produced in the opening 9 is thrown into a light guide plate 11 mounted on the upper surface of the mother board 8, thereby illuminating the liquid crystal display from the back surface thereof.
In the conventional light emitting diode 1, however, since the light emitting element 5 is directly mounted on the upper surface of the first electrode 3, a distance L1 from the upper surface of the light emitting element 5 to a light receiving surface of the light guide plate 11 becomes large, which reduces a spreading angle xcex81 of the incoming light introduced from the light emitting element 5 into the light guide plate 11. This in turn reduces the amount of light entering the light guide plate 11, making it difficult to increase a brightness of the liquid crystal display screen.
An object of the present invention is to provide a light emitting diode which, when used as a backlight source for a liquid crystal display, reduces a distance from a light emitting element to a light receiving surface of a light guide plate to increase the spreading angle of the light introduced from the light emitting element into the light guide plate and also increase the amount of light entering the light guide plate, thus enhancing the level of brightness of the liquid crystal display.
To achieve the above objective, the light emitting diode of the present invention comprises:
a mother board having an opening;
a pair of electrodes arranged on one surface of the mother board;
a light guide plate arranged on the other surface of the mother board;
a light emitting element arranged in the opening of the mother board and mounted to one of the pair of electrodes; and
a positioning means mounted on the one electrode to position the light emitting element close to the light guide plate.
In this construction, since the light emitting element can be put close to the light guide plate by the positioning means provided on one of the electrodes, the light emitted from the light emitting element can be led out over a wide spreading angle although the light emitting element is installed in the opening of the mother board.
The pair of electrodes are attached to a substrate and an assembly of the electrodes and the substrate is secured to the mother board.
The positioning means has a spacer interposed between the one electrode and the light emitting element. This spacer has the simplest form of the positioning means.
Further, the positioning means is capable of adjusting the position of the light emitting element so as to change the position of the light emitting element relative to the light guide plate. Thus, adjusting the position of the light emitting element relative to the light guide plate can select a desired spreading angle of the light introduced from the light emitting element into the light guide plate.
Further, the positioning means comprises a plurality of replaceable spacers with different heights so that replacing the spacer with a desired one can change the position of the light emitting element relative to the light guide plate.
Further, the positioning means comprises a plurality of washers arranged between the light emitting element and the one electrode. By increasing or reducing the number of washers, the height of the positioning means can easily be adjusted.
Further, the positioning means comprises a screw member screwed into the substrate, and the screw member has a mounting portion on which to mount the light emitting element and a screw portion extending from the mounting portion. With this construction, the positioning means can easily change the position of the light emitting element relative to the light guide plate.
An electrical conduction is established between the one electrode and the spacer and between the spacer and the light emitting element.
The spacer is made from a conductive material. Thus, the electrical conduction between the one electrode and the light emitting element can easily be obtained through the spacer.
Further, the spacer is made from an insulating material. Thus, an insulation between the light emitting element and the one electrode can be secured by the spacer.
Further, the spacer has a reflection surface. This provides an increased level of brightness.
Further, the spacer comprises a core made of plastics or glass and a conductive metal plating provided on an outer surface of the core.
Further, the positioning means comprises a stepped portion formed by projecting a light emitting element mounting portion of the one electrode toward the light guide plate. This obviates the need for the spacer.
These features and advantages of the present invention will be described in more detail by referring to the accompanying drawings.